This invention relates generally to apparatus and methods for perforating material, and a perforated material produced thereby, and more specifically to apparatus and methods for perforating webs of thin flat material such as paper, and a perforated material produced thereby.
Thin flat materials such as paper are frequently perforated in order to create a line of weakness along which the paper can be torn from a continuous web, into individual sheets. However, the apparatus of the present invention is particularly related to the perforation of paper used as backing for fabric as it is being processed into apparel or the like (referred to in the industry as "kraft" paper). In automated processing of fabric, multiple layers of fabric are frequently held in a stack such as for cutting a pattern from the fabric. In this way, multiple workpieces of fabric can be formed with a single cutting stroke through the layers. The stack of fabric is held in place by suction acting on the bottom layer of the stack. The fabric is air permeable so that the suction is experienced by all of the layers of the stack. A backing of kraft paper is applied to each layer of fabric before processing to protect the bottom layer from dirt, to provide a uniform air permeability for all types of fabric so that the same suction can be applied to hold the fabric, and to prevent adjacent layers of fabric including some polymeric materials from welding together during the cutting process.
Kraft paper available from the paper manufacturer is not substantially air permeable. Therefore, so that the paper will be more air permeable, it is perforated to provide openings for passage of air through the paper. The openings must be formed in a uniform manner over the surface area of the paper, and in such a fashion that they do not close up upon the application of suction. In the past, openings have been formed by punching out generally circular pieces of the paper. The process of punching out the openings is slow and produces a large amount of debris (i.e., the circular punch outs). Presently, the perforating process approximately doubles the cost of the kraft paper to the end user.